Inverurie to Insch redoubling was supposed to be the next phase of the A2I project after the Berryden to Inverurie redoubling but they ran out of money then Covid intervened. From Inverurie to Keith the double track solum and earthworks are still complete, there is only one major structure (Deveron Viaduct) which was extensively refurbished and strengthened in summer 2023, and the minor over and under bridges are all still configured for double track. You’d need to do something with Oyne and Gartly AHB crossings as these both date from 1973 but are due for renewal at some point in CP7 anyway. You could argue all day whether the signalling between Aberdeen and Elgin would be better recontrolled to a new workstation in Aberdeen or if the Highland workstation in Inverness could cope with the increase.
However, the line is geographically distant from the Central Belt and to date the Scottish Government has shown little interest in the needs and aspirations of the north of Scotland. There is also the ongoing saga of the (non) dualling of the A96 road between Inverurie and Inverness, which looks to be going the same way as the A9 ill-fated dualling project. There is also the fact that the Scottish Government is skint and the offical appetite for infrastructure investment - let alone enhancement - is likely to be minimal over the next decade.
In short - don’t hold your breath.
